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Secular changes in New Zealand rainfall characteristics 1950-2009

Current climate model projections suggest a warming climate will correspond to higher precipitation rates, as well as more frequent extreme rainfall events. Using daily rainfall from eight stations around New Zealand, we compare changes across two thirty year periods (1950-1979 and 1980-2009). We focus on changes in total annual precipitation, numbers of days with recorded rainfall, the intensity of these rainfall events and the mean seasonal cycle at each station. Our preliminary results show a pattern of rainfall decrease in the north and rainfall increase in the southwest, with matching changes to the number of rain days at some stations. While changes to overall daily rainfall total distributions are generally small, there is a strong correlation between changes in total annual rainfall and the frequency of heavy rain days. Further work is needed to understand the internal characteristics of future precipitation patterns with continued climate change. However, these results support current scenarios for New Zealand of rainfall decreases in the northern half of the North Island and increases in the west and south of the South Island.